1.
Day
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In common usage, it is either an interval equal to 24 hours or daytime, the consecutive period of time during which the Sun is above the horizon. The period of time during which the Earth completes one rotation with respect to the Sun is called a solar day, several definitions of this universal human concept are used according to context, need and convenience. In 1960, the second was redefined in terms of the motion of the Earth. The unit of measurement day, redefined in 1960 as 86400 SI seconds and symbolized d, is not an SI unit, but is accepted for use with SI. The word day may also refer to a day of the week or to a date, as in answer to the question. The life patterns of humans and many species are related to Earths solar day. In recent decades the average length of a day on Earth has been about 86400.002 seconds. A day, understood as the span of time it takes for the Earth to make one rotation with respect to the celestial background or a distant star, is called a stellar day. This period of rotation is about 4 minutes less than 24 hours, mainly due to tidal effects, the Earths rotational period is not constant, resulting in further minor variations for both solar days and stellar days. Other planets and moons have stellar and solar days of different lengths to Earths, besides the day of 24 hours, the word day is used for several different spans of time based on the rotation of the Earth around its axis. An important one is the day, defined as the time it takes for the Sun to return to its culmination point. Because the Earth orbits the Sun elliptically as the Earth spins on an inclined axis, on average over the year this day is equivalent to 24 hours. A day, in the sense of daytime that is distinguished from night-time, is defined as the period during which sunlight directly reaches the ground. The length of daytime averages slightly more than half of the 24-hour day, two effects make daytime on average longer than nights. The Sun is not a point, but has an apparent size of about 32 minutes of arc, additionally, the atmosphere refracts sunlight in such a way that some of it reaches the ground even when the Sun is below the horizon by about 34 minutes of arc. So the first light reaches the ground when the centre of the Sun is still below the horizon by about 50 minutes of arc, the difference in time depends on the angle at which the Sun rises and sets, but can amount to around seven minutes. Ancient custom has a new day start at either the rising or setting of the Sun on the local horizon, the exact moment of, and the interval between, two sunrises or sunsets depends on the geographical position, and the time of year. A more constant day can be defined by the Sun passing through the local meridian, the exact moment is dependent on the geographical longitude, and to a lesser extent on the time of the year
2.
Roman timekeeping
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The Roman clock, or time of day, was divided into 24 hours,12 hours of light and 12 hours of darkness. Since the length of the sunlight varied with the seasons, this meant that the length of the hour changed - with shorter hours in winter and longer hours in summer. The Romans also understood that the length of daylight depended upon latitude, at the winter solstice, at mediterranean latitude, an hour was about 45 minutes, while at the summer solstice, an hour was about 75 minutes. Since local habits varied across the empire, local Roman habits also varied, in particular, whether the day started from sunrise, or later midnight, or from sunset as Athenians and Jews. The Romans also divided the day into other periods, such as media noctis inclinatio midnight, gallicinium cock-crow, conticinium hush of the night, the Jewish and early Christian subjects of the empire often had different methods of timekeeping. The Roman civil and religious day began at midnight from an early time. Yet following classic Roman thinking, Jack Finegan argues that the hour can be counted from midnight. He maintained this position despite not having any evidence at all, as an explanation, he referenced the time in which Jesus was at Pilate and the time in which he was crucified. Consequently, he argued that because of such supposed Roman time, for example, the Gospel of John makes reference to Pilate having said behold your king to the people of Jerusalem at the sixth hour. To indicate that it is a day or night hour Romans used expressions such as for example prima diei hora, the Romans divided the night into four watches, following the Greek practice, since, as Vegetius explains, a city-guard could not stand watch all night. For example, in the watch of night meant just before dawn. According to many sources each watch consisted of three of the twelve listed previously night hours, the Romans used various timekeeping devices including the clepsydra, or water clock, and the Greek sundial. Censorinus describes the introduction of sundials to Rome by Manius Valerius after his victories in Sicily, though the comparison is with the speakers young days when a child is free of timekeeping, not about the introduction of sundials. Marcus Vitruvius Pollio lists various types of sundials in Book IX of his De Architectura, the Roman day starting at dawn survives today in the Spanish word siesta, literally the sixth hour of the day. The English term noon is derived from the ninth hour. Telling Time in Ancient Rome Article Hora in William Smiths Dictionary of Greek & Roman Antiquities Romanvoices hour conversion tables
3.
Sunset
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Sunset or sundown, is the daily disappearance of the Sun below the horizon as a result of Earths rotation. The Sun will set exactly due west at the equator on the spring and fall equinoxes, the time of sunset is defined in astronomy as the moment when the trailing edge of the Suns disk disappears below the horizon. Dusk is at the end of astronomical twilight, and is the darkest moment of twilight just before night. Sunset creates unique atmospheric conditions such as the intense orange and red colors of the Sun. The time of sunset varies throughout the year, and is determined by the position on Earth, specified by longitude and latitude. During winter and spring, the days get longer and sunsets occur later every day until the day of the latest sunset, in the Northern Hemisphere, the latest sunset occurs late in June or in early July, but not on the summer solstice of June 21. This date depends on the viewers latitude, likewise, the earliest sunset does not occur on the winter solstice, but rather about two weeks earlier, again depending on the viewers latitude. In the Northern Hemisphere, it occurs in early December or late November, for a few weeks surrounding both solstices, both sunrise and sunset get slightly later each day. Even on the equator, sunrise and sunset shift several minutes back and forth through the year and these effects are plotted by an analemma. Sunsets occur almost exactly due west on the equinoxes for all viewers on Earth, exact calculations of the azimuths of sunset on other dates are complex, but they can be estimated with reasonable accuracy by using the analemma. As sunrise and sunset are calculated from the leading and trailing edges of the Sun, respectively, and not the center, the duration of a daytime is slightly longer than nighttime. Further, because the light from the Sun is refracted as it passes through the Earths atmosphere, refraction also affects the apparent shape of the Sun when it is very close to the horizon. It makes things appear higher in the sky than they really are, light from the bottom edge of the Suns disk is refracted more than light from the top, since refraction increases as the angle of elevation decreases. This raises the apparent position of the edge more than the top. Its width is unaltered, so the disk appears wider than it is high, the Sun also appears larger on the horizon, an optical illusion, similar to the moon illusion. Because the shorter wavelength components, such as blue and green, scatter more strongly, the remaining reddened sunlight can then be scattered by cloud droplets and other relatively large particles to light up the horizon red and orange. The removal of the wavelengths of light is due to Rayleigh scattering by air molecules and particles much smaller than the wavelength of visible light. The scattering by cloud droplets and other particles with diameters comparable to or larger than the sunlights wavelengths is due to Mie scattering and is not strongly wavelength-dependent
4.
Sunrise
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Sunrise or sun up is the instant at which the upper edge of the Sun appears over the horizon in the morning. The term can refer to the entire process of the Sun crossing the horizon. Although the Sun appears to rise from the horizon, it is actually the Earths motion that causes the Sun to appear, architect Buckminster Fuller proposed the terms sunsight and sunclipse to better represent the heliocentric model, though the terms have not entered into common language. Astronomically, sunrise occurs for only an instant, the moment at which the limb of the Sun appears tangent to the horizon. However, the term commonly refers to periods of time both before and after this point, Twilight, the period in the morning during which the sky is light. The beginning of morning twilight is called dawn, the period after the Sun rises during which striking colors and atmospheric effects are still seen. Sunrise occurs before the Sun actually reaches the horizon because the Suns image is refracted by the Earths atmosphere, at the horizon, the average amount of refraction is 34 arcminutes, though this amount varies based on atmospheric conditions. Also, unlike most other measurements, sunrise occurs when the Suns upper limb, rather than its center. The apparent radius of the Sun at the horizon is 16 arcminutes and these two angles combine to define sunrise to occur when the Suns center is 50 arcminutes below the horizon, or 90. 83° from the zenith. The timing of sunrise varies throughout the year and is affected by the viewers longitude and latitude, altitude. The analemma can be used to make predictions of the time of sunrise. In late winter and spring, sunrise as seen from temperate latitudes occurs earlier each day, reaching its earliest time near the summer solstice, after this point, the time of sunrise gets later each day, reaching its latest sometime around the winter solstice. Variations in atmospheric refraction can alter the time of sunrise by changing its apparent position, near the poles, the time-of-day variation is exaggerated, since the Sun crosses the horizon at a very shallow angle and thus rises more slowly. Accounting for atmospheric refraction and measuring from the leading edge slightly increases the duration of day relative to night. Sunrises occur approximately due east on the March and September equinoxes for all viewers on Earth, exact calculations of the azimuths of sunrise on other dates are complex, but they can be estimated with reasonable accuracy by using the analemma. Air molecules and airborne particles scatter white sunlight as it passes through the Earths atmosphere and this is done by a combination of Rayleigh scattering and Mie scattering. Because the shorter wavelength components, such as blue and green, scatter more strongly, the remaining reddened sunlight can then be scattered by cloud droplets and other relatively large particles to light up the horizon red and orange. The removal of the wavelengths of light is due to Rayleigh scattering by air molecules and particles much smaller than the wavelength of visible light
5.
Season
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A season is a division of the year marked by changes in weather, ecology and hours of daylight. Seasons result from the orbit of the Earth around the Sun. During May, June, and July, the northern hemisphere is exposed to direct sunlight because the hemisphere faces the sun. The same is true of the hemisphere in November, December. It is the tilt of the Earth that causes the Sun to be higher in the sky during the months which increases the solar flux. However, due to lag, June, July, and August are the hottest months in the northern hemisphere and December, January. In temperate and subpolar regions, four calendar-based seasons are recognized, spring, summer, autumn or fall. Ecologists often use a model for temperate climate regions, prevernal, vernal, estival, serotinal, autumnal. Many tropical regions have two seasons, the rainy, wet, or monsoon season and the dry season, some have a third cool, mild, or harmattan season. Seasons often held special significance for agrarian societies, whose lives revolved around planting and harvest times, in some parts of the world, some other seasons capture the timing of important ecological events such as hurricane season, tornado season, and wildfire season. The most historically important of these are the three seasons—flood, growth, and low water—which were previously defined by the annual flooding of the Nile in Egypt. The seasons result from the Earths axis of rotation being tilted with respect to its orbital plane by an angle of approximately 23.5 degrees, regardless of the time of year, the northern and southern hemispheres always experience opposite seasons. This is because during summer or winter, one part of the planet is directly exposed to the rays of the Sun than the other. For approximately half of the year, the northern hemisphere tips toward the Sun, for the other half of the year, the same happens, but in the southern hemisphere instead of the northern, with the maximum around December 21. The two instants when the Sun is directly overhead at the Equator are the equinoxes. Also at that moment, both the North Pole and the South Pole of the Earth are just on the terminator, and hence day and night are equally divided between the northern and southern hemispheres. Around the March equinox, the northern hemisphere will be experiencing spring as the hours of daylight increase, the effect of axial tilt is observable as the change in day length and altitude of the Sun at noon during a year. Between this effect and the daylight hours, the axial tilt of the Earth accounts for most of the seasonal variation in climate in both hemispheres
6.
Noon
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Noon is usually defined as 12 oclock in the daytime, as opposed to midnight. The term midday is also used colloquially to refer to a period of time in the middle of the day. Solar noon is when the Sun transits the celestial meridian and is at its highest altitude in the sky. The local or clock time of solar noon depends on the longitude, the opposite of noon is midnight. In many cultures in the Northern Hemisphere, noon had ancient geographic associations with the direction south, remnants of the noon = south association are preserved in the words for noon in French and Italian, both of which also refer to the southern parts of the respective countries. Modern Polish, Belarusian, Ukrainian, and Serbian go a step farther, with the words for noon also meaning south, the word noon is derived from Latin nona hora, the ninth hour of the day, and is related to the liturgical term none. The Roman and Western European medieval monastic day began at 6,00 a. m. at the equinox by modern timekeeping, in English, the meaning of the word shifted to midday and the time gradually moved back to 12,00 local time. The change began in the 12th century and was fixed by the 14th century, solar noon is the moment when the Sun transits the celestial meridian – roughly the time when it is highest above the horizon on that day. This is also the origin of the ante meridiem and post meridiem as noted below. The sun is overhead at solar noon at the Equator on the equinoxes, at the Tropic of Cancer on the June solstice. The elapsed time from local solar noon of one day to the day is exactly 24 hours only four instances in any particular year. This occurs when the effects of Earth’s obliquity of ecliptic and its orbital speed around the Sun offset each other and these four days for the current epoch are centered about Feb 11, May 13, July 25 and Nov 3. It occurs at one particular line of Longitude each event. This line varies year to year since Earth’s true year is not a number of days. This event time and location also varies due to Earth’s orbit being gravitationally perturbed by the planets and these four 24-hour days occur in both N and S hemispheres simultaneously. The precise UTC times for four days also mark when the opposite line of longitude 180 degrees away experiences precisely 24 hours from local midnight to local midnight the next day. Thus four varying great circles of Longitude define from year to year when a 24-hour day occurs, the two longest time spans from noon to noon occur twice each year around Jun 20 and around Dec 21. The shortest time spans occur twice each year around March 25, noon is commonly indicated by 12 p. m. and midnight by 12 a. m
7.
Antisolar point
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The antisolar point is the imaginary point on the celestial sphere exactly opposite the Sun from the viewpoint of an observer. This means that the point lies above the horizon when the Sun is below it. On a sunny day, the point can be easily found. The antisolar point forms the center of several optical phenomena, including rainbows, glories. Occasionally, during sunset or sunrise, anticrepuscular rays can be seen to converge at the point near the horizon. This is an illusion, however, caused by perspective. In reality, the rays run parallel to each other, also, on a moonless night away from city lights, it is often possible to see the gegenschein at that point, arising from the back-scattering of light by interplanetary dust. In astronomy, when the moon or planets are in opposition, the anthelic point is often used as a synonym for the antisolar point, but the two should be differentiated. There are several phenomena that are centered on or converge on the anthelic point, such as the anthelion, Wegener arcs, Tricker arcs
8.
Meridian (astronomy)
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In astronomy, the meridian is the great circle passing through the celestial poles, the zenith, and the nadir of an observers location. Consequently, it also the horizons north and south points. A celestial meridian matches the projection of a terrestrial meridian onto the celestial sphere, hence, the number of astronomical meridians are infinite. There are several ways in which the meridian can be divided into semicircles, in one way, it is divided into the local meridian and the antimeridian. The former semicircle contains the zenith and is terminated by the celestial poles, in the horizontal coordinate system the meridian is divided into halves terminated by the horizons north and south points. The upper meridian passes through the zenith, and the lower meridian, a celestial object will appear to drift past the local meridian as the Earth spins, for the meridian is fixed to the local horizon. At culmination, the object reaches its highest point in the sky when crossing, or transiting, using an objects right ascension and the local sidereal time it is possible to determine the time of its culmination. The term meridian comes from the Latin meridies, which means both midday and south, meridian Prime meridian Longitude Millar, William. The Amateur Astronomers Introduction to the Celestial Sphere
9.
Nadir
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The nadir, is the direction pointing directly below a particular location, that is, it is one of two vertical directions at a specified location, orthogonal to a horizontal flat surface there. Since the concept of being below is itself somewhat vague, scientists define the nadir in more rigorous terms. Specifically, in astronomy, geophysics and related sciences, the nadir at a point is the local vertical direction pointing in the direction of the force of gravity at that location. The direction opposite of the nadir is the zenith, the word is also used figuratively to mean the lowest point of a persons spirits, or the quality of an activity or profession. The term nadir can also be used to represent the lowest point reached by a body during its apparent orbit around a given point of observation. This can be used to describe the location of the Sun, the sun is said to be at the nadir at a location when it is at the zenith at the locations antipode and the sun is 90 degrees below the horizon. In oncology, the nadir is used to represent the lowest level of a blood cell count while a patient is undergoing chemotherapy. A diagnosis of neutropenic nadir after chemotherapy typically lasts 7–10 days
10.
Night
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Night or nighttime is the period of time between the sunset and the sunrise when the Sun is below the horizon. Complete darkness or astronomical night is the period of time between astronomical dusk and astronomical dawn when the sun is between 18 and 90 degrees below the horizon and the sky is totally dark, at latitudes between 48.5 and 66. The opposite of night is day, the start and end points of time for a night vary, based on factors such as season, latitude, longitude and timezone. Twilight is the time of night when the sky is illuminated by the sun but the sun is below the horizon. At any given time, one side of the planet Earth is bathed in light from the Sun and this shadow is called the umbra. Natural illumination is provided by a combination of moonlight, planetary light, starlight, diffuse zodiacal light, gegenschein. In some circumstances, bioluminescence, aurorae, and lightning can provide some illumination, the glow provided by artificial illumination is sometimes referred to as light pollution because it can interfere with observational astronomy and ecosystems. Nights are shorter than days on average due to two factors, firstly, the sun is not a point, but has an apparent size of about 32 arc minutes. Secondly, the atmosphere refracts sunlight so that some of it reaches the ground when the sun is below the horizon by about 34 arc minutes. The combination of two factors means that light reaches the ground when the center of the sun is below the horizon by about 50 arc minutes. Without these effects, day and night would be the length at the autumnal and vernal equinoxes. In reality, around the equinoxes the day is almost 14 minutes longer than the night at the equator, the summer and winter solstices mark the shortest and the longest night, respectively. The closer a location is to either the North Pole or the South Pole, in the Northern Hemisphere, Denmark has shorter nights in June than India. In the Southern Hemisphere, Antarctica has longer nights in June than Chile, the phenomenon of day and night is due to the rotation of a celestial body about its axis, creating an illusion of the sun rising and setting. Different bodies spin at different rates, however. Some may spin much faster than Earth, while others spin extremely slowly, leading to long days. The planet Venus rotates once every 224.7 days – by far the slowest rotation period of any of the major planets, in contrast, the gas giant Jupiters sidereal day is only 9 hours and 56 minutes. Mercury has the longest day-night cycle as a result of its 3,2 resonance between its orbital period and rotation period - this resonance gives it a day-night cycle 176 days long
11.
Dusk
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Dusk occurs at the darkest stage of twilight, or at the very end of astronomical twilight after sunset and just before night. The term dusk usually refers to astronomical dusk, or the darkest part of twilight before night begins. The time of dusk is the moment at the end of astronomical twilight, just before total darkness or night. Civil twilight, the first phase of twilight, ends when the sun is 6 degrees below the horizon in the evening, at this time objects are still distinguishable and depending on weather conditions some stars and planets may start to become visible to the naked eye. Nautical twilight, the phase of twilight, ends when the sun is 12 degrees below the horizon in the evening. At this time, objects are less distinguishable, and stars, astronomical twilight, the final phase of twilight, ends when the sun is 18 degrees below the horizon in the evening. At this time the sun no longer illuminates the sky, and thus no longer interferes with astronomical observations
12.
Dawn
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Dawn or astronomical dawn is the time that marks, depending on the specific usage, the beginning of the twilight before sunrise, the period of the pre-sunrise twilight or the time of sunrise. When identified as the beginning of or the period of twilight, it is recognized by the presence of weak sunlight, different definitions exist for the start of dawn. The difference between these definitions is the amount of sunlight that must be present and this occurs when the Sun is 18 degrees below the horizon in the morning. Though it is possible to localize the direction of the Sun during astronomical dawn and dusk, astronomical dawn and dusk are night, the zenith is extremely dark and more than just the brightest stars can be seen. Nautical Dawn is still dark and is considered night. At civil dawn there is darkness and at the zenith. The sky is still a bit dark and civil dawn is still considered night, at all places on the earth, dawn and dusk times are fastest around the equinoxes and slowest at the summer and winter solstices. As the calendar approaches the summer or winter solstice, the days or nights, respectively, get longer, which can have a potential impact on the time and duration of dawn and dusk. This effect is pronounced closer to the poles, where the Sun rises at the spring equinox and sets at the autumn equinox, with a long period of dawn/dusk. The polar circle is defined as the lowest latitude at which the Sun does not set at the summer solstice, therefore, the angular radius of the polar circle is equal to the angle between the plane of Earths equator and that of the ecliptic. This period of time with no sunset lengthens closer to the pole, near the summer solstice, latitudes higher than 54°30′ get no darker than nautical dawn/dusk, the darkness of the night varies greatly in these latitudes. At latitudes higher than about 59°20, summer nights get no darker than civil dusk or dawn and this period of bright nights is longer at higher latitudes. When the sun gets 9.0 to 9.5 degrees below the horizon, many Indo-European mythologies have a dawn goddess, separate from the male Solar deity, her name deriving from PIE *h2ausos-, derivations of which include Greek Eos, Roman Aurora and Indian Ushas. Also related is Lithuanian Aušrinė, and possibly a Germanic *Austrōn-, in Sioux mythology, Anpao is an entity with two faces. The Hindu dawn deity Ushas is female, whereas Surya, the Sun, and Aruṇa, Ushas is one of the most prominent Rigvedic deities. The time of dawn is also referred to as the Brahmamuhurtham, in some parts of India, both Usha and Pratyusha are worshiped along with the Sun during the festival of Chhath. Prime is the time of prayer of the traditional Divine Office in Christian liturgy. In Islam, astronomical dawn is the time of the first prayer of the day, in Judaism, the question of how to calculate dawn is posed by the Talmud, as it is has many ramifications for Jewish law
13.
Meridian (geography)
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A meridian is the half of an imaginary great circle on the Earths surface, terminated by the North Pole and the South Pole, connecting points of equal longitude. The position of a point along the meridian is given by its latitude indicating how many degrees north or south of the Equator the point is, each meridian is perpendicular to all circles of latitude. Each is also the length, being half of a great circle on the Earths surface. Most maps show the lines of longitude, the position of the prime meridian has changed a few times throughout history, mainly due to the transit observatory being built next door to the previous one. Such changes had no significant practical effect, historically, the average error in the determination of longitude was much larger than the change in position. The adoption of WGS84 as the system has moved the geodetic prime meridian 102.478 metres east of its last astronomic position. The position of the current geodetic prime meridian is not identified at all by any kind of sign or marking in Greenwich, but can be located using a GPS receiver. The term meridian comes from the Latin meridies, meaning midday, the same Latin stem gives rise to the terms a. m. and p. m. used to disambiguate hours of the day when utilizing the 12-hour clock. Therefore, a compass needle will be parallel to the magnetic meridian, the angle between the magnetic and the true meridian is the magnetic declination, which is relevant for navigating with a compass. Searchable PDF prepared by the author, C. A. White, resources page of the U. S. Department of the Interior, Bureau of Land Management Meridian
14.
Daylight saving time
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Daylight saving time is the practice of advancing clocks during summer months by one hour so that evening daylight lasts an hour longer, while sacrificing normal sunrise times. Typically, regions that use Daylight Savings Time adjust clocks forward one hour close to the start of spring, American inventor and politician Benjamin Franklin proposed a form of daylight time in 1784. New Zealander George Hudson proposed the idea of saving in 1895. The German Empire and Austria-Hungary organized the first nationwide implementation, starting on April 30,1916, many countries have used it at various times since then, particularly since the energy crisis of the 1970s. The practice has both advocates and critics, DST clock shifts sometimes complicate timekeeping and can disrupt travel, billing, record keeping, medical devices, heavy equipment, and sleep patterns. Computer software often adjusts clocks automatically, but policy changes by various jurisdictions of DST dates, industrialized societies generally follow a clock-based schedule for daily activities that do not change throughout the course of the year. The time of day that individuals begin and end work or school, North and south of the tropics daylight lasts longer in summer and shorter in winter, with the effect becoming greater as one moves away from the tropics. However, they will have one hour of daylight at the start of each day. Supporters have also argued that DST decreases energy consumption by reducing the need for lighting and heating, DST is also of little use for locations near the equator, because these regions see only a small variation in daylight in the course of the year. After ancient times, equal-length civil hours eventually supplanted unequal, so civil time no longer varies by season, unequal hours are still used in a few traditional settings, such as some monasteries of Mount Athos and all Jewish ceremonies. This 1784 satire proposed taxing window shutters, rationing candles, and waking the public by ringing church bells, despite common misconception, Franklin did not actually propose DST, 18th-century Europe did not even keep precise schedules. However, this changed as rail transport and communication networks came to require a standardization of time unknown in Franklins day. Modern DST was first proposed by the New Zealand entomologist George Hudson, whose shift work job gave him time to collect insects. An avid golfer, he also disliked cutting short his round at dusk and his solution was to advance the clock during the summer months, a proposal he published two years later. The proposal was taken up by the Liberal Member of Parliament Robert Pearce, a select committee was set up to examine the issue, but Pearces bill did not become law, and several other bills failed in the following years. Willett lobbied for the proposal in the UK until his death in 1915, william Sword Frost, mayor of Orillia, Ontario, introduced daylight saving time in the municipality during his tenure from 1911 to 1912. Starting on April 30,1916, the German Empire and its World War I ally Austria-Hungary were the first to use DST as a way to conserve coal during wartime, Britain, most of its allies, and many European neutrals soon followed suit. Russia and a few other countries waited until the year
15.
Northern Hemisphere
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The Northern Hemisphere is the half of Earth that is north of the equator. For other planets in the Solar System, north is defined as being in the celestial hemisphere relative to the invariable plane of the solar system as Earths North pole. Due to the Earths axial tilt, winter in the Northern Hemisphere lasts from the December solstice to the March Equinox, the dates vary each year due to the difference between the calendar year and the astronomical year. Its surface is 60. 7% water, compared with 80. 9% water in the case of the Southern Hemisphere, the Arctic is the region north of the Arctic Circle. Its climate is characterized by cold winters and cool summers, precipitation mostly comes in the form of snow. The Arctic experiences some days in summer when the Sun never sets, the duration of these phases varies from one day for locations right on the Arctic Circle to several months near the North Pole, which is the middle of the Northern Hemisphere. Between the Arctic Circle and the Tropic of Cancer lies the Northern Temperate Zone, the changes in these regions between summer and winter are generally mild, rather than extreme hot or cold. However, a temperate climate can have very unpredictable weather, tropical regions are generally hot all year round and tend to experience a rainy season during the summer months, and a dry season during the winter months. In the Northern Hemisphere, objects moving across or above the surface of the Earth tend to turn to the right because of the coriolis effect, as a result, large-scale horizontal flows of air or water tend to form clockwise-turning gyres. These are best seen in circulation patterns in the North Atlantic. For the same reason, flows of air down toward the surface of the Earth tend to spread across the surface in a clockwise pattern. Thus, clockwise air circulation is characteristic of high pressure weather cells in the Northern Hemisphere, conversely, air rising from the northern surface of the Earth tends to draw air toward it in a counterclockwise pattern. Hurricanes and tropical storms spin counter-clockwise in the Northern Hemisphere, the shadow of a sundial moves clockwise in the Northern Hemisphere. When viewed from the Northern Hemisphere, the Moon appears inverted compared to a view from the Southern Hemisphere, the North Pole faces away from the galactic center of the Milky Way. The Northern Hemisphere is home to approximately 6.57 billion people which is around 90% of the total human population of 7.3 billion people
16.
North
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North is one of the four cardinal directions or compass points. It is the opposite of south and is perpendicular to east and west, North is a noun, adjective, or adverb indicating direction or geography. The word north is related to the Old High German nord, the Latin word borealis comes from the Greek boreas north wind, north, which, according to Ovid, was personified as the son of the river-god Strymon, the father of Calais and Zetes. Septentrionalis is from septentriones, the seven plow oxen, a name of Ursa Maior, the Greek ἀρκτικός is named for the same constellation, and is the source of the English word Arctic. For example, in Lezgian, kefer can mean both disbelief and north, since to the north of the Muslim Lezgian homeland there are areas formerly inhabited by non-Muslim Caucasian, in many languages of Mesoamerica, north also means up. The direction north is associated with colder climates because most of the worlds land at high latitudes is located in the Northern Hemisphere. By convention, the top side of a map is often north, to go north using a compass for navigation, set a bearing or azimuth of 0° or 360°. North is specifically the direction that, in Western culture, is treated as the fundamental direction, on any rotating non-astronomical object, north denotes the side appearing to rotate counter-clockwise when viewed from afar along the axis of rotation. Magnetic north is of interest because it is the direction indicated as north on a properly functioning magnetic compass, the difference between it and true north is called the magnetic declination. But simple generalizations on the subject should be treated as unsound, maps intended for usage in orienteering by compass will clearly indicate the local declination for easy correction to true north. Maps may also indicate grid north, which is a term referring to the direction northwards along the grid lines of a map projection. The visible rotation of the sky around the visible celestial pole provides a vivid metaphor of that direction corresponding to up. Thus the choice of the north as corresponding to up in the hemisphere, or of south in that role in the southern, is, prior to worldwide communication, anything. On the contrary, it is of interest that Chinese and Islamic culture even considered south as the top end for maps. Up is a metaphor for north, the notion that north should always be up and east at the right was established by the Greek astronomer Ptolemy. While the choice of north over south as prime direction reflects quite arbitrary historical factors and their folk definitions are, respectively, where the sun rises and where it sets. The true folk-astronomical definitions of east and west are the directions, an angle from the prime direction. Being the default direction on the compass, north is referred to frequently in Western popular culture, some examples include, The phrase north of X is often used by Americans to mean more than X or greater than X, i. e
17.
South
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South is a noun, adjective, or adverb indicating direction or geography. It is one of the four directions or compass points. South is the polar opposite of north and is perpendicular to east and west, the word south comes from Old English sūþ, from earlier Proto-Germanic *sunþaz, possibly related to the same Proto-Indo-European root that the word sun derived from. By convention, the side of a map is south. To go south using a compass for navigation, set a bearing or azimuth of 180°, alternatively, in the Northern Hemisphere outside the tropics, the Sun will be roughly in the south at midday. True south is the direction towards the end of the axis about which the earth rotates. The South Pole is located in Antarctica, magnetic south is the direction towards the south magnetic pole, some distance away from the south geographic pole. Roald Amundsen, from Norway, was the first to reach the South Pole, on 14 December 1911, the Global South refers to the socially and economically less-developed southern half of the globe. 95% of the Global North has enough food and shelter, in the South, on the other hand, only 5% of the population has enough food and shelter. It lacks appropriate technology, it has no political stability, the economies are disarticulated, in the card game bridge, one of the players is known for scoring purposes as South. South partners with North and plays against East and West, in Greek religion, Notos, was the south wind and bringer of the storms of late summer and autumn. The dictionary definition of south at Wiktionary
18.
Polish language
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Polish is a West Slavic language spoken primarily in Poland and is the native language of the Poles. It belongs to the Lechitic subgroup of the West Slavic languages, Polish is the official language of Poland, but it is also used throughout the world by Polish minorities in other countries. It is one of the languages of the European Union. Its written standard is the Polish alphabet, which has 9 additions to the letters of the basic Latin script, Polish is closely related to Kashubian, Silesian, Upper Sorbian, Lower Sorbian, Czech and Slovak. It is also the second most widely spoken Slavic language, after Russian, in history, Polish is known to be an important language, both diplomatically and academically in Central and Eastern Europe. Today, Polish is spoken by over 38.5 million people as their first language in Poland. It is also spoken as a language in western parts of Belarus and Ukraine, west and central Lithuania, as well as the northern parts of the Czech Republic. There are 55 million Polish language speakers around the world, Polish began to emerge as a distinct language around the 10th century, the process largely triggered by the establishment and development of the Polish state. With Christianity, Poland also adopted the Latin alphabet, which made it possible to write down Polish, the precursor to modern Polish is the Old Polish language. Ultimately, Polish is thought to descend from the unattested Proto-Slavic language, Poland is the most linguistically homogeneous European country, nearly 97% of Polands citizens declare Polish as their first language. Elsewhere, Poles constitute large minorities in Lithuania, Belarus, Polish is the most widely used minority language in Lithuanias Vilnius County and is found elsewhere in southeastern Lithuania. There are significant numbers of Polish speakers among Polish emigrants and their descendants in many other countries, in the United States, Polish Americans number more than 11 million but most of them cannot speak Polish fluently. The largest concentrations of Polish speakers reported in the census were found in three states, Illinois, New York, and New Jersey. Enough people in these areas speak Polish that PNC Financial Services offer services available in Polish at all of their machines in addition to English and Spanish. According to the 2011 census there are now over 500,000 people in England, in Canada, there is a significant Polish Canadian population, There are 242,885 speakers of Polish according to the 2006 census, with a particular concentration in Toronto and Montreal. The geographical distribution of the Polish language was affected by the territorial changes of Poland immediately after World War II. Poles settled in the Recovered Territories in the west and north and this tendency toward a homogeneity also stems from the vertically integrated nature of the authoritarian Polish Peoples Republic. The inhabitants of different regions of Poland still speak standard Polish somewhat differently, first-language speakers of Polish have no trouble understanding each other, and non-native speakers may have difficulty distinguishing regional variations
19.
Belarusian language
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Belarusian is an official language of Belarus, along with Russian, and is spoken abroad, chiefly in Russia, Ukraine, and small parts in far-eastern Poland. Following independence, it became known as Belarusian. Belarusian is one of the East Slavic languages and shares many grammatical and lexical features with other members of the group, to some extent, Russian, Ukrainian, and Belarusian are mutually intelligible. Its predecessor stage is known as Ruthenian, in turn descended from Old East Slavic, at the 1999 Belarus Census, the Belarusian language was declared as a language spoken at home by about 3,686,000 Belarusian citizens. About 6,984,000 of Belarusians declared it their mother tongue, other sources put the population of the language as 6,715,000 in Belarus and 9,081,102 in all countries. According to a study done by the Belarusian government in 2009, 72% of Belarusians speak Russian at home,29. 4% of Belarusians can write, speak, and read Belarusian, while 52. 5% can only read and speak it. Although closely related to other East Slavic languages, especially Ukrainian, Belarusian phonology is distinct in a number of ways, the phoneme inventory of the modern Belarusian language consists of 45 to 54 phonemes,6 vowels and 39 to 48 consonants, depending on how they are counted. When the nine geminate consonants are excluded as mere variations, there are 39 consonants, the number 48 includes all consonant sounds, including variations and rare sounds, which may be semantically distinct in the modern Belarusian language. The Belarusian alphabet is a variant of the Cyrillic script, which was first used as an alphabet for the Old Church Slavonic language, the modern Belarusian form was defined in 1918, and consists of thirty-two letters. Before that, Belarusian had also written in the Belarusian Latin alphabet, the Belarusian Arabic alphabet. The Glagolitic script had been used, sporadically, until the 11th or 12th century, there are several systems of romanizing written Belarusian text in existence, see Romanization of Belarusian. Standardized Belarusian grammar in its form was adopted in 1959. It was developed from the form set down by Branislaw Tarashkyevich. Historically, there had existed several other alternative standardized forms of Belarusian grammar and it is mainly based on the Belarusian folk dialects of Minsk-Vilnius region. Belarusian grammar is mostly synthetic and partly analytic, and overall is similar to Russian grammar. The most significant instance of this is in the representation of vowel reduction, and in particular akannye, the merger of unstressed /a/ and /o/, Belarusian always spells this merged sound as ⟨a⟩, whereas Russian uses either ⟨a⟩ or ⟨o⟩, according to what the underlying phoneme is. This can significantly complicate the task of foreign speakers in learning these paradigms, besides the literary norm, there exist two main dialects of the Belarusian language, the North-Eastern and the South-Western. In addition, there exist the transitional Middle Belarusian dialect group, the North-Eastern dialect is chiefly characterized by the soft sounding R and strong akanye, and the South-Western dialect is chiefly characterized by the hard sounding R and moderate akanye
20.
Ukrainian language
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Ukrainian /juːˈkreɪniən/ is an East Slavic language. Written Ukrainian uses a variant of the Cyrillic script, historical linguists trace the origin of the Ukrainian language to the Old East Slavic of the early medieval state of Kievan Rus. After the fall of the Kievan Rus as well as the Kingdom of Galicia–Volhynia, the Modern Ukrainian language has been in common use since the late 17th century, associated with the establishment of the Cossack Hetmanate. From 1804 until the Russian Revolution, the Ukrainian language was banned from schools in the Russian Empire and it has always maintained a sufficient base in Western Ukraine, where the language was never banned, in its folklore songs, itinerant musicians, and prominent authors. The Ukrainian language retains a degree of intelligibility with Belarusian and Russian. The first theory of the origin of Ukrainian language was suggested in Imperial Russia in the middle of the 18th century by Mikhail Lomonosov and this theory posits the existence of a common language spoken by all East Slavic people in the time of the Rus. Another point of view developed during the 19th and 20th centuries by linguists of Imperial Russia, like Lomonosov, they assumed the existence of a common language spoken by East Slavs in the past. This general point of view is the most accepted amongst academics worldwide, the supporters of this theory disagree, however, about the time when the different languages were formed. Soviet scholars set the divergence between Ukrainian and Russian only at time periods. During the time of the incorporation of Ruthenia into the Polish–Lithuanian Commonwealth and this point of view is, however, at variance with some historical data. In fact, several East Slavic tribes, such as Polans, Drevlyans, Severians, Dulebes, White Croats, Tiverians, notably, some Ukrainian features were recognizable in the southern dialects of Old East Slavic as far back as the language can be documented. In contrast, Ahatanhel Krymsky and Alexei Shakhmatov assumed the existence of the spoken language of Eastern Slavs only in prehistoric times. According to their point of view, the diversification of the Old East Slavic language took place in the 8th or early 9th century, Ukrainian linguist Stepan Smal-Stotsky went even further, denying the existence of a common Old East Slavic language at any time in the past. Similar points of view were shared by Yevhen Tymchenko, Vsevolod Hantsov, Olena Kurylo, Ivan Ohienko, according to this theory, the dialects of East Slavic tribes evolved gradually from the common Proto-Slavic language without any intermediate stages during the 6th through 9th centuries. The Ukrainian language was formed by convergence of tribal dialects, mostly due to a migration of the population within the territory of todays Ukraine in later historical periods. This point of view was supported by George Shevelovs phonological studies. During the 13th century, when German settlers were invited to Ukraine by the princes of Galicia-Vollhynia and their influence would continue under Poland not only through German colonists but also through the Yiddish-speaking Jews. Often such words involve trade or handicrafts, examples of words of German or Yiddish origin spoken in Ukraine include dakh, rura, rynok, kushnir, and majster
21.
Serbian language
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Serbian is the standardized variety of the Serbo-Croatian language mainly used by Serbs. It is the language of Serbia and one of the three official languages of Bosnia and Herzegovina. In addition, it is a minority language in Montenegro, Croatia, Macedonia, Romania, Hungary, Slovakia. Standard Serbian is based on the most widespread dialect of Serbo-Croatian, Shtokavian, which is also the basis of Standard Croatian, Bosnian, the other dialect spoken by Serbs is Torlakian in southeastern Serbia, which is transitional to Macedonian and Bulgarian. Serbian is practically the only European standard language with complete synchronic digraphia, the Serbian Cyrillic alphabet was devised in 1814 by Serbian linguist Vuk Karadžić, who created the alphabet on phonemic principles. The Latin alphabet was designed by Croatian linguist Ljudevit Gaj in 1830, Serbian is a standardized variety of Serbo-Croatian, a Slavic language, of the South Slavic subgroup. Other standardized forms of Serbo-Croatian are Bosnian, Croatian, and Montenegrin and it has lower intelligibility with the Eastern South Slavic languages Bulgarian and Macedonian, than with Slovene. The 2011 census show that 42. 88% still declare Serbian to be their native language, Standard Serbian language uses both Cyrillic and Latin script. Even in official government documents this constitutional requirement is rarely enforced, Serbian is a rare example of synchronic digraphia, a situation where all literate members of a society have two interchangeable writing systems available to them. Media and publishers typically select one alphabet or another, for example, the public broadcaster, Radio Television of Serbia, predominantly uses the Cyrillic script whereas the privately run broadcasters, like RTV Pink, predominantly use the Latin script. A survey from 2014 showed that 47% of the Serbian population favors the Latin alphabet whereas 36% favors the Cyrillic one and these are the tenses of the indicative mood. Apart from the mood, there is also the imperative mood. The conditional mood has two more tenses, the first conditional and the second conditional, Serbian has active and passive voice. As for the verb forms, Serbian has one infinitive. Most Serbian words are of native Slavic lexical stock, tracing back to the Proto-Slavic language, there are many loanwords from different languages, reflecting cultural interaction throughout history. Notable loanwords were borrowed from Greek, Latin, Italian, Turkish, Hungarian, Russian, Serbian literature emerged in the Middle Ages, and included such works as Miroslavljevo jevanđelje in 1192 and Dušanov zakonik in 1349. In the mid-15th century, Serbia was conquered by the Ottoman Empire, however, some of the greatest literary works in Serbian come from this time, in the form of oral literature, the most notable form being Serbian epic poetry. The epic poems were written down in the 19th century, and preserved in oral tradition up to the 1950s
22.
12-hour clock
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The 12-hour clock is a time convention in which the 24 hours of the day are divided into two periods, a. m. and p. m. Each period consists of 12 hours numbered,12,1,2,3,4,5,6,7,8,9,10, and 11. The 24 hour/day cycle starts at 12 midnight, runs through 12 noon, the 12-hour clock was developed over time from the mid-second millennium BC to the 16th century AD. The natural day- and night division of a calendar day forms the basis as to why each day is split into two cycles. Originally there were two cycles, one cycle which could be tracked by the position of the Sun followed by one cycle which could be tracked by the Moon and this would eventually evolve into the two 12-hour periods that started at midnight and noon which are used today. Noon itself is rarely abbreviated today, but if it is, the 12-hour clock can be traced back as far as Mesopotamia and Ancient Egypt. Both an Egyptian sundial for daytime use and an Egyptian water clock for night-time use were found in the tomb of Pharaoh Amenhotep I, dating to c.1500 BC, these clocks divided their respective times of use into 12 hours each. The Romans also used a 12-hour clock, daylight was divided into 12 equal hours, in Northern Europe these dials generally used the 12-hour numbering scheme in Roman numerals, but showed both a. m. and p. m. periods in sequence. This is known as the system, and can be seen on many surviving clock faces, such as those at Wells. Elsewhere in Europe, particularly in Italy, numbering was more likely to be based on the 24-hour system, the 12-hour clock was used throughout the British empire. During the 15th and 16th centuries, the 12-hour analog dial, the 24-hour analog dial was reserved for more specialized applications, such as astronomical clocks and chronometers. Most analog clocks and watches use the 12-hour dial, on which the shorter hour hand rotates once every 12 hours. Some analog clock dials have a ring of numbers along with the standard 1-to-12 numbered ring. The number 12 is paired either with a 00 or a 24, while the numbers 1 through 11 are paired with the numbers 13 through 23 and this modification allows the clock to be read also in the 24-hour notation. This kind of 12-hour clock can be found in countries where the 24-hour clock is preferred, in several countries the 12-hour clock is the dominant written and spoken system of time. Other countries use the 12-hour clock mainly in spoken time, while the 24-hour notation is written, in most countries the 12-hour clock is used in speech alongside the 24-hour clock. The 12-hour clock in speech often uses such as in the morning, in the afternoon, in the evening. Outside of English-speaking countries, the terms a. m. and p. m. are seldom used and often unknown
23.
24-hour clock
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The 24-hour clock is the convention of time keeping in which the day runs from midnight to midnight and is divided into 24 hours, indicated by the hours passed since midnight, from 0 to 23. This system is the most commonly used time notation in the world today, in the practice of medicine, the 24-hour clock is generally used in documentation of care as it prevents any ambiguity as to when events occurred in a patients medical history. It is popularly referred to as time in the United States. In the case of a second, the value of ss may extend to 60. A leading zero is added for numbers under 10 and this zero is optional for the hours, but very commonly used in computer applications, where many specifications require it. Where subsecond resolution is required, the seconds can be a fraction, that is. The most commonly used separator symbol between hours, minutes and seconds is the colon, which is also the used in ISO8601. In the past, some European countries used the dot on the line as a separator, in some contexts, no separator is used and times are written as, for example,2359. In East Asia, time notation was 24-hour before westernization in modern times, the clocks were changed into 12 dual-hours style when they were shipped to China in the Qing dynasty. In the 24-hour time notation, the day begins at midnight,00,00, and the last minute of the day begins at 23,59. Where convenient, the notation 24,00 may also be used to refer to midnight at the end of a given date – that is,24,00 of one day is the time as 00,00 of the following day. The notation 24,00 mainly serves to refer to the end of a day in a time interval. A typical usage is giving opening hours ending at midnight, similarly, some railway timetables show 00,00 as departure time and 24,00 as arrival time. Legal contracts often run from the date at 00,00 until the end date at 24,00. While the 24-hour notation unambiguously distinguishes between midnight at the start and end of any date, there is no commonly accepted distinction among users of the 12-hour notation. Sometimes the use of 00,00 is also avoided, in variance with this, the correspondence manual for the U. S. Navy and U. S. Marine Corps formerly specified 0001 to 2400. The manual was updated in June 2015 to use 0000 to 2359, time-of-day notations beyond 24,00 are not commonly used and not covered by the relevant standards. In most countries, computers by default show the time in 24-hour notation, for example, Microsoft Windows and macOS activate the 12-hour notation by default only if a computer is in a handful of specific language and region settings
24.
Hebrew calendar
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The Hebrew or Jewish calendar is a lunisolar calendar used today predominantly for Jewish religious observances. It determines the dates for Jewish holidays and the public reading of Torah portions, yahrzeits. The present Hebrew calendar is the product of evolution, including a Babylonian influence, when to add it was based on observation of natural agriculture-related events in Israel. Through the Amoraic period and into the Geonic period, this system was displaced by the mathematical rules used today. The principles and rules were codified by Maimonides in the Mishneh Torah in the 12th century. Maimonides work also replaced counting years since the destruction of the Temple with the modern creation-era Anno Mundi, the era used since the Middle Ages is the Anno Mundi epoch. As with Anno Domini, the words or abbreviation for Anno Mundi for the era should properly precede the date rather than follow it, AM5777 began at sunset on 2 October 2016 and will end at sunset on 20 September 2017. The Jewish day is of no fixed length, the Jewish day is modeled on the reference to. there was evening and there was morning. In the creation account in the first chapter of Genesis, based on the classic rabbinic interpretation of this text, a day in the rabbinic Hebrew calendar runs from sunset to the next sunset. In most populated parts of the world this is always approximately 24 standard hours, halachically, a day ends and a new one starts when three stars are visible in the sky. The time between sunset and the time when the three stars are visible is known as bein hashmashot, and there are differences of opinion as to which day it falls into for some uses. This may be relevant, for example, in determining the date of birth of a child born during that gap, there is no clock in the Jewish scheme, so that the local civil clock is used. The civil clock is used only as a reference point – in expressions such as, Shabbat starts at. In Judaism, an hour is defined as 1/12 of the time from sunrise to sunset, so, during the winter, an hour can be less than 60 minutes. This proportional hour is known as a shaah zmanit, a Jewish hour is divided into 1080 halakim or parts. A part is 3⅓ seconds or 1/18 minute, the ultimate ancestor of the helek was a small Babylonian time period called a barleycorn, itself equal to 1/72 of a Babylonian time degree. These measures are not generally used for everyday purposes, instead of the international date line convention, there are varying opinions as to where the day changes. One opinion uses the antimeridian of Jerusalem, the weekdays start with Sunday and proceed to Saturday, Shabbat
25.
Islamic calendar
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The Islamic, Muslim, or Hijri calendar is a lunar calendar consisting of 12 months in a year of 354 or 355 days. It is used to date events in many Muslim countries and it is also used by Muslims to determine the proper days of Islamic holidays and rituals, such as the annual period of fasting and the proper time for the pilgrimage to Mecca. The Islamic calendar employs the Hijri era whose epoch was retrospectively established as the Islamic New Year of AD622, during that year, Muhammad and his followers migrated from Mecca to Yathrib and established the first Muslim community, an event commemorated as the Hijra. In the West, dates in this era are usually denoted AH in parallel with the Christian, in Muslim countries, it is also sometimes denoted as H from its Arabic form. In English, years prior to the Hijra are reckoned as BH, the current Islamic year is 1438 AH. In the Gregorian calendar,1438 AH runs from approximately 3 October 2016 to 21 September 2017, four of the twelve Hijri months are considered sacred, Rajab, and the three consecutive months of Dhū al-Qa‘dah, Dhu al-Ḥijjah and Muḥarram. As the lunar calendar lags behind the solar calendar by about ten days every gregorian year, the cycle repeats every 33 lunar years. Each month of the Islamic calendar commences on the birth of the new lunar cycle, traditionally this is based on actual observation of the crescent marking the end of the previous lunar cycle and hence the previous month, thereby beginning the new month. Consequently, each month can have 29 or 30 days depending on the visibility of the moon, astronomical positioning of the earth and weather conditions. However, certain sects and groups, most notably Dawoodi Bohra Muslims and Shia Ismaili Muslims, use a tabular Islamic calendar in which odd-numbered months have thirty days, in Arabic, the first day of the week corresponds with Sunday of the planetary week. The Islamic weekdays, like those in the Hebrew and Baháí calendars, the Christian liturgical day, kept in monasteries, begins with vespers, which is evening, in line with the other Abrahamic traditions. Christian and planetary weekdays begin at the following midnight, Muslims gather for worship at a mosque at noon on gathering day which corresponds with Friday. Thus gathering day is regarded as the weekly day of rest. A few others have adopted the Saturday-Sunday weekend while making Friday a working day with a midday break to allow time off for worship. Inscriptions of the ancient South Arabian calendars reveal the use of a number of local calendars, at least some of these calendars followed the lunisolar system. For Central Arabia, especially Mecca, there is a lack of epigraphical evidence, both al-Biruni and al-Masudi suggest that the Ancient Arabs used the same month names as the Muslims, though they also record other month names used by the pre-Islamic Arabs. Nevertheless, the Islamic position equating Nisan with Dhū al-Ḥijja has prevailed, for a comparison between the Islamic and pre-Islamic months, see Islamic and Jahili months. The Islamic tradition is unanimous in stating that Arabs of Tihamah, Hejaz, the forbidden months were four months during which fighting is forbidden, listed as Rajab and the three months around the pilgrimage season, Dhu al-Qa‘dah, Dhu al-Hijjah, and Muharram
26.
New Year's Eve
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In the Gregorian calendar, New Years Eve, the last day of the year, is on December 31 which is the seventh day of the Christmas season. In many countries, New Years Eve is celebrated at evening gatherings, where many people dance, eat, drink alcoholic beverages. Some Christians attend a watchnight service, the celebrations generally go on past midnight into January 1. Samoa, Tonga and Kiritimati, part of Kiribati, are the first places to welcome the New Year while American Samoa, New Year traditions and celebrations in Canada vary regionally. New Years Eve is generally a social holiday, in some areas, such as in rural Quebec, people ice fish in the old days. Since 2000, the highlight of New Years Eve celebrations is in Montreals old port, which comes alive with concerts that take place and fireworks at midnight. From 1956 to 1976, Guy Lombardo and his Royal Canadians serenaded Canada on the CBC, via a feed from CBS, after Lombardos death in 1977, the Royal Canadians continued on CBC and CBS until 1978. Following the finale of the series, the original cast continued to participate in New Years Eve specials in the years following. Similarly, the CBCs French language network Ici Radio-Canada Télé airs its own yearly New Years Eve comedy special, Bye Bye. Unlike Year of the Farce, Bye Bye has been presented by comedians, originally running from 1968 to 1998. Mexicans celebrate New Years Eve, by eating a grape with each of the chimes of a clocks bell during the midnight countdown. Mexican sweet bread is baked with a coin or charm hidden in the dough, when the bread is served, the recipient of the slice with the coin or charm is said to be blessed with good luck in the New Year. At the same time, they are expressed for all the good things during the year that is ending so that they continue in the new year. Mexicans celebrate with a dinner with their families, the traditional meal being turkey or pork loin. Afterwards many people attend parties outside the home, for example, in Mexico City there is a street festival on New Years Eve centered on the Zocalo, the citys main square. Celebrations include firecrackers, fireworks and sparklers and shouts of ¡Feliz Año Nuevo, in Puerto Rico, New Years Eve is celebrated with friends and family. The Puerto Rico Convention Center in San Juan is the attraction for Puerto Ricans during the celebration. It has Latin music and fireworks at midnight along with the signature song Auld Lang Syne in Spanish, in the United States, New Years Eve is celebrated with formal parties, family-oriented activities, and other large public events
27.
National Institute of Standards and Technology
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The National Institute of Standards and Technology is a measurement standards laboratory, and a non-regulatory agency of the United States Department of Commerce. Its mission is to promote innovation and industrial competitiveness, in 1821, John Quincy Adams had declared Weights and measures may be ranked among the necessities of life to every individual of human society. From 1830 until 1901, the role of overseeing weights and measures was carried out by the Office of Standard Weights and Measures, president Theodore Roosevelt appointed Samuel W. Stratton as the first director. The budget for the first year of operation was $40,000, a laboratory site was constructed in Washington, DC, and instruments were acquired from the national physical laboratories of Europe. In addition to weights and measures, the Bureau developed instruments for electrical units, in 1905 a meeting was called that would be the first National Conference on Weights and Measures. Quality standards were developed for products including some types of clothing, automobile brake systems and headlamps, antifreeze, during World War I, the Bureau worked on multiple problems related to war production, even operating its own facility to produce optical glass when European supplies were cut off. Between the wars, Harry Diamond of the Bureau developed a blind approach radio aircraft landing system, in 1948, financed by the Air Force, the Bureau began design and construction of SEAC, the Standards Eastern Automatic Computer. The computer went into operation in May 1950 using a combination of vacuum tubes, about the same time the Standards Western Automatic Computer, was built at the Los Angeles office of the NBS and used for research there. A mobile version, DYSEAC, was built for the Signal Corps in 1954, due to a changing mission, the National Bureau of Standards became the National Institute of Standards and Technology in 1988. Following 9/11, NIST conducted the investigation into the collapse of the World Trade Center buildings. NIST had a budget for fiscal year 2007 of about $843.3 million. NISTs 2009 budget was $992 million, and it also received $610 million as part of the American Recovery, NIST employs about 2,900 scientists, engineers, technicians, and support and administrative personnel. About 1,800 NIST associates complement the staff, in addition, NIST partners with 1,400 manufacturing specialists and staff at nearly 350 affiliated centers around the country. NIST publishes the Handbook 44 that provides the Specifications, tolerances, the Congress of 1866 made use of the metric system in commerce a legally protected activity through the passage of Metric Act of 1866. NIST is headquartered in Gaithersburg, Maryland, and operates a facility in Boulder, nISTs activities are organized into laboratory programs and extramural programs. Effective October 1,2010, NIST was realigned by reducing the number of NIST laboratory units from ten to six, nISTs Boulder laboratories are best known for NIST‑F1, which houses an atomic clock. NIST‑F1 serves as the source of the official time. NIST also operates a neutron science user facility, the NIST Center for Neutron Research, the NCNR provides scientists access to a variety of neutron scattering instruments, which they use in many research fields
28.
Twilight
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Twilight is the illumination of the Earths lower atmosphere when the Sun itself is not directly visible because it is below the horizon. Twilight is produced by scattering in the upper atmosphere, illuminating the lower atmosphere so that the surface of the Earth is neither completely lit nor completely dark. The word twilight is also used to denote the periods of time when this illumination occurs, the further the Sun is below the horizon, the dimmer the twilight. When the Sun reaches 18 degrees below the horizon, the brightness is nearly zero. When the Sun again reaches 18 degrees below the horizon, nighttime becomes morning twilight, Twilight should not be confused with auroras, which can have a similar appearance in the night sky at high latitudes. By analogy with evening twilight, the word twilight is also used metaphorically, to imply that something is losing strength. For example, very old people may be said to be in the twilight of their lives, the collateral adjective for twilight is crepuscular which is sometimes applied to insects, fish, and mammals that are most active during that time. Twilight is defined according to the elevation angle θs, which is the position of the geometric center of the sun relative to the horizon. There are three established and widely accepted subcategories of twilight, civil twilight, nautical twilight, and astronomical twilight. Morning civil twilight begins when the center of the sun is 6° below the horizon. Evening civil twilight begins at sunset or when the center of the sun is 0°50′ below the horizon. In the United States military, the initialisms BMCT and EECT are used to refer to these periods, morning nautical twilight begins and evening nautical twilight ends when the geometric center of the sun reaches 12° below the horizon. Morning astronomical twilight begins and Evening astronomical twilight ends when the center of the Sun reaches 18° below the horizon. There are three established and widely accepted subcategories of twilight, civil twilight, nautical twilight, and astronomical twilight, under clear weather conditions, civil twilight approximates the limit at which solar illumination suffices for the human eye to clearly distinguish terrestrial objects. Enough sunlight renders artificial sources unnecessary for most outdoor activities, at civil dawn, the beginning of morning civil twilight, and at civil dusk, the end of evening civil twilight, sunlight clearly defines the horizon while the brightest stars and planets can appear. As observed from the Earth, sky-gazers know Venus, the brightest planet, law-makers have enshrined the concept of civil twilight. Such statutes typically use a period after sunset or before sunrise. The period may affect when pilots require a rating to fly aircraft
29.
Morning
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Morning is the period of time between midnight and 11,59 am or, more commonly, the interval between sunrise and noon. Morning precedes afternoon, evening, and night in the sequence of a day, originally, the term referred to sunrise. The words “morning” and “tomorrow” began in Middle English as morwening, developing into morwen, then morwe, English uniquely separates “morning” and “tomorrow, ” despite their common root. Other languages, like Spanish and German, have one word – mañana and morgen, according to Max Weber, “Morning” takes on another meaning, specifically, “the size of land strip which an ox could plow in a day without giving out. As such, a “good morning” could mean “a good day’s plow. ”Some languages that use the time of day in greeting have a special greeting for morning, such as the English good morning. The appropriate time to use such greetings, such as whether it may be used between midnight and dawn, depends on the cultures or speakers concept of morning. Morning typically encompasses the prerequisites for full productivity and life in public, such as bathing, eating a meal such as breakfast, dressing and it may also include information activities, such as planning the days schedule or reading a morning newspaper. The boundaries of such morning periods are by necessity idiosyncratic, for some, the word morning may refer to the period immediately following waking up, irrespective of the current time of day. This modern sense of morning is due largely to the spread of electricity. The morning period may be a period of enhanced or reduced energy, the ability of a person to wake up effectively in the morning may be influenced by a gene called Period 3. This gene comes in two forms, a long and a short variant and it seems to affect the persons preference for mornings or evenings. People who carry the long variant were over-represented as morning people, while the carrying the short variant were evening preference people. Quotations related to Morning at Wikiquote The dictionary definition of morning at Wiktionary Good Morning Images
30.
Daytime
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On Earth, daytime is roughly the period on any given point of the planets surface during which it experiences natural illumination from indirect or direct sunlight. Other planets that rotate in relation to a primary, such as a local star, also experience daytime of a sort. Approximately half of the Earth is illuminated at any time by the Sun, the hemisphere of the Earth experiencing daytime at any given instant changes continuously as the planet rotates on its own axis. The axis of the Earths rotation is not perpendicular to the plane of its orbit around the Sun, additionally, since the axis of rotation is relatively fixed in comparison to the stars, it moves with respect to the Sun as the planet orbits the star. This creates seasonal variations in the length of the period at most points on the planets surface. Because the Sun is a disc as seen from the Earth, rather than a point source of light, sunrise and sunset are not instantaneous. Additionally, the Earths atmosphere further bends and diffuses light from the Sun and lengthens the period of sunrise, for a certain period after sunset and before sunrise, indirect light from the Sun lightens the sky on Earth, this period is often referred to as twilight. Certain groups, such as Earthly astronomers, do not consider daytime to be ended until the Suns disc is actually well below the Earths horizon. Areas experiencing summer are tilted toward the sun, while increased daylight can have some effect on the increased temperature in the summer, most of the increase in temperature is due to the directness of the sun, not the increased daylight. The high angles of the sun is what causes the tropics to be warm while low angles at the poles is what causes them to be cold. Although the length of the period is always twelve hours at the Equator, in all seasons. During the winter, the period is shorter than twelve hours, during the summer. When it is north of the Equator, it is summer south of the Equator. At the Equator, the period is always almost twelve hours in length. The sun always rises nearly perpendicular to the horizon, from the March Equinox to the September Equinox, it rises a bit north of east, and sets a bit north of west. From the September Equinox to the March Equinox, it rises a bit south of east, the fact that the Sun is always so close to the vertical at noon on the Equator explains why equatorial regions are the hottest regions on the planet overall. The tropics occupy a band of the Earths surface between 23. 5° north latitude and 23. 5° south latitude, within this band, the Sun will pass almost directly overhead on at least one day per year. The line of 23. 5° north latitude is called the Tropic of Cancer, because when it was named, the equivalent line of south latitude is called the Tropic of Capricorn, for similar reasons
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Belt of Venus
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The Belt of Venus or Venuss Girdle or Twilight Wedge is an atmospheric phenomenon seen shortly before sunrise or shortly after sunset. The observer is, or is nearly, surrounded by a pinkish glow that extends roughly 10°–20° above the horizon. Like alpenglow, backscattering of reddened sunlight also creates the Belt of Venus, in a way, the Belt of Venus is a true alpenglow visible at twilight near the anti-solar point. Often, the glow is separated from the horizon by a dark layer, the archs light pink color is due to backscattering of reddened light from the rising or setting Sun. A very similar effect can be seen during a solar eclipse. The zodiacal light, which is caused by reflection of sunlight from the interplanetary dust in the system, is also a similar phenomenon. The name of the phenomenon alludes to the cestus, a girdle or breast-band, of the Ancient Greek goddess Aphrodite, anticrepuscular rays Atmospheric refraction Blue hour Earths shadow Golden hour or Magic hour Naylor, John. Out of the blue, a 24-hour skywatchers guide, scroll to the very bottom of the post to view, after all other Yosemite panoramas
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Blue hour
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This effect is caused by the relative diffusibility of short blue wavelengths of light versus the longer red wavelengths. During the blue hour, red light passes straight into space while blue light is scattered in the atmosphere and therefore reaches the earths surface, many artists treasure this period because of the quality of the light. The blue hour is famous for its connotations, particularly in the arts. A colloquial French saying characterises the blue hour as a time of confusion and mystery, as a result of the perceived specialness of this time, there are various restaurants, theatres and hotels called LHeure Bleue located worldwide. There is also a womens perfume by Guerlain of the same name, the blue hour has now been largely abolished in England, Scotland and Wales in favour of all-day opening
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Golden hour (photography)
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In photography, the golden hour is a period shortly after sunrise or before sunset during which daylight is redder and softer than when the Sun is higher in the sky. More blue light is scattered, so if the sun is present, in addition, the suns small angle with the horizon produces longer shadows. The term hour is used figuratively, the effect has no clearly defined duration and varies according to season and latitude. The character of the lighting is determined by the altitude, and the time for the sun to move from the horizon to a specified altitude depends on a locations latitude. In Los Angeles, California, at an hour after sunrise or an hour before sunset, the sun has an altitude of about 10°–12°. For a location closer to the equator, the altitude is reached in less than an hour, and for a location farther from the equator. For a location far from the equator, the sun may not reach an altitude of 10°. In the middle of the day, the bright sun can create strong highlights. The degree to which overexposure can occur varies because different types of film, because the contrast is less during the golden hour, shadows are less dark, and highlights are less likely to be overexposed. In landscape photography, the color of the low sun is often considered desirable to enhance the colours of the scene. Film director Terrence Malick has used this technique in such as Days of Heaven, The New World. The Robert Redford directed film The Milagro Beanfield War made extensive use of the hour in its location filming. Blue hour Alpenglow Belt of Venus Golden Hour Calculator Twilight Calculator – Blue Hour / Golden Hour Table
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Terminator (solar)
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A terminator or twilight zone is a moving line that separates the illuminated day side and the dark night side of a planetary body. A terminator is defined as the locus of points on a moon or planet where the line through its sun is tangent, on Earth, the terminator is a circle with a diameter that is approximately that of the Earth. The circle separates the portion of the Earth experiencing daylight from that experiencing darkness, at the equator, under flat conditions, the terminator moves at approximately 1668 kilometers per hour. The speed of the terminator decreases as it approaches the poles, supersonic aircraft like jet fighters or Concorde and Tupolev Tu-144 supersonic transports are the only aircraft able to overtake the maximum speed of the terminator. However, slower vehicles can overtake the terminator at higher latitudes, the visual effect is that of seeing the sun rise in the west, or set in the east. Amateur radio operators take advantage of conditions at the terminator to perform long distance communications, under good conditions, radio waves can travel along the terminator to antipodal points. This is primarily because the D layer, which high frequency signals. This process is known as skywave propagation, the Lunar terminator is the division between the illuminated and dark parts of the Moon. It is the equivalent of the division between night and day on the Earths sphere, although the Moons much lower rate of rotation means it takes longer for it to pass across the surface. Due to the angle at which sunlight strikes this portion of the moon, shadows cast by craters and other features are elongated. This phenomenon is similar to the lengthening of shadows on Earth when the sun is low in the sky, for this reason, much lunar photographic study centers on the illuminated area near the lunar terminator, and the resulting shadows provide accurate descriptions of the terrain. Examination of a terminator can yield information about the surface of a body, for example. As the particles within an atmosphere are at a higher elevation and these particles scatter the light, reflecting some of it to the ground. Hence, the sky can remain illuminated even after the sun has set, low Earth orbit satellites take advantage of the fact that certain polar orbits set near the terminator do not suffer from eclipse, therefore their solar cells are continuously lit by sunlight. Such orbits are called dawn-dusk orbits, a type of Sun-synchronous orbit and this prolongs the operational life of a LEO satellite, as onboard battery life is prolonged. It also enables specific experiments that require minimum interference from the Sun, as the designers can opt to install the relevant sensors on the dark side of the satellite
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Daylight
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Daylight, or the light of day, is the combination of all direct and indirect sunlight during the daytime. This includes direct sunlight, diffuse sky radiation, and both of these reflected from the Earth and terrestrial objects, sunlight scattered or reflected from objects in outer space is not generally considered daylight. Thus, moonlight is never considered daylight, despite being indirect sunlight, daytime is the period of time each day when daylight occurs. Daylight happens because the Earth rotates and either side the sun shines on is considered daylight, daylight is present at a particular location, to some degree, whenever the sun is above the horizon at that location. It may be darker under unusual circumstances such as an eclipse or very high levels of atmospheric smoke, dust. For comparison, nighttime levels are, For a table of approximate daylight intensity in the Solar System. Daylighting is lighting an indoor space with such as windows. This type of lighting is chosen to save energy, to avoid hypothesized adverse health effects of over-illumination by artificial light, the amount of daylight received into an indoor space or room is defined as a daylight factor, being the ratio between the measured internal and external light levels. In recent years, work has taken place to recreate the effects of daylight artificially and this is however expensive in terms of both equipment and energy consumption and is applied almost exclusively in specialist areas such as filmmaking, where light of such intensity is required anyway. In some filmmaking locations, such as Sweden, there is too much light due to summer days. As a result, in films like Marianne, night scenes have to be shot during the daylight hours. Http, //www. gandraxa. com/length_of_day. xml Deriving the formulas to calculate the length of day
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Afternoon
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Afternoon is the time of the day between noon and evening. It is the time when the sun is descending from its zenith in the sky to somewhat before its terminus at the horizon in the west direction, in human life, it occupies roughly the latter half of the standard work and school day. It is usually from 12 PM to 4 PM, but in countries it may be from 12 PM to 8 PM. Afternoon is the time occurring between noon and evening, the word afternoon, which derives from after and noon, has been attested from about the year 1300, Middle English contained both afternoon and the synonym aftermete. The standard locative marking for the word was at afternoon in the fifteenth and sixteenth centuries but has shifted to in the afternoon since then, in Southern U. S. and Midland American English, the word evening is sometimes used to encompass all times between noon and night. The Irish language contains four different words to mark time intervals from late afternoon to nightfall, metaphorically, the word afternoon refers to a relatively late period in the expanse of time or in ones life. The term should not be confused with after noon, which is a translation of the Latin post meridiem, Afternoon is a time when the sun is descending from its daytime peak. During the afternoon, the sun moves from roughly the center of the sky to deep in the west, in late afternoon, sunlight is particularly bright and glaring, because the sun is at a low angle in the sky. Schools usually let out during the afternoon as well, however, cortisol levels are also the most reactive to environmental changes unrelated to sleep and daylight during the afternoon. As a result, this time of day is considered optimal for researchers studying stress, plants generally have their highest photosynthetic levels of the day at noon and in the early afternoon, owing to the suns high angle in the sky. In humans, body temperature is typically highest during the mid to late afternoon, however, human athletes being tested for physical vigor on exercise machines showed no statistically significant difference after lunch. When these animals are too hot, they are likely to become belligerent. The afternoon, especially the early afternoon, is associated with a dip in a variety of areas of cognitive and productive functioning. Notably, motor vehicle accidents occur frequently in the early afternoon. A study of accidents in Sweden between 1987 and 1991 found that the time around 5 pm had by far the most accidents. This trend may have influenced by the afternoon rush hour. In Finland, accidents in the industry are most common in the afternoon. One psychology professor studying circadian rhythms found that his students performed worse on exams in the afternoon than in the morning
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Midnight sun
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The midnight sun is a natural phenomenon that occurs in the summer months in places north of the Arctic Circle or south of the Antarctic Circle, when the sun remains visible at the local midnight. Around the summer solstice the sun is visible for the full 24 hours, the number of days per year with potential midnight sun increases the farther towards either pole one goes. A quarter of Finlands territory lies north of the Arctic Circle, in Svalbard, Norway, the northernmost inhabited region of Europe, there is no sunset from approximately 19 April to 23 August. The extreme sites are the poles, where the sun can be visible for half the year. The opposite phenomenon, polar night, occurs in winter, when the sun stays below the horizon throughout the day, since the axial tilt of the Earth is considerable, the sun does not set at high latitudes in local summer. The duration of sunlight increases from one day during the solstice at the polar circle, to several weeks only 100 km closer to the pole. At extreme latitudes, the sun is usually referred to as polar day. At the poles themselves, the sun rises and sets only once each year, for example, Iceland is known for its midnight sun, even though most of it is slightly south of the Arctic Circle. For the same reasons, the period of sunlight at the poles is slightly longer than six months, even the northern extremities of Scotland experience twilight in the northern sky at around the summer solstice. Observers at heights appreciably above sea level can experience extended periods of midnight sun as a result of the dip of the horizon viewed from altitude, the term midnight sun refers to the consecutive 24-hour periods of sunlight experienced north of the Arctic Circle and south of the Antarctic Circle. Other phenomena are sometimes referred to as midnight sun, but they are caused by time zones, for instance, in Fairbanks, Alaska, which is south of the Arctic Circle, the sun sets at 12,47 am at the summer solstice. This is because Fairbanks is 51 minutes ahead of its time zone. This means that solar culmination occurs at about 1,51 pm instead of at 12 noon, if a precise moment for the genuine midnight sun is required, the observers longitude, the local civil time and the equation of time must be taken into account. The moment of the suns closest approach to the horizon coincides with its due north at the observers position. These two effects must be added, furthermore, the equation of time must be added, a positive value on a given date means that the sun is running slightly ahead of its average position, so the value must be subtracted. The equation of time at that date is -2.0 minutes, therefore, the suns lowest elevation occurs 120 -103.2 +2.0 minutes after midnight, at 00.19 Central European Summer time. On other nearby dates the only thing different is the equation of time, the suns altitude remains within half a degree of the minimum of about 5 degrees for about 45 minutes either side of this time. The midnight sun is visible at the Arctic Circle from 12 June until 1 July and this period extends as one travels north, At Cape Nordkinn, Norway, the northernmost point of Continental Europe, the midnight sun lasts approximately from 14 May to 29 July
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Polar night
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The polar night occurs when the night lasts for more than 24 hours. This occurs only inside the polar circles, the opposite phenomenon, the polar day, or midnight sun, occurs when the Sun stays above the horizon for more than 24 hours. Night is understood as the center of the Sun being below a free horizon. Since the atmosphere bends the rays of the Sun, the day is longer than the polar night. The polar circle is located at a latitude between two areas, at the latitude of approximately 66.5 degrees. In the most northern city of Sweden, Kiruna, at 67°51N, while it is day in the Arctic Circle it is night in the Antarctic Circle. The polar shortest day is not totally dark everywhere inside the circle, but only in places within about 5° of the poles. Regions located at the border of the polar circles experience polar twilight instead of polar night. In fact, polar regions typically get more twilight throughout the year than equatorial regions, however, not all this time is classified as polar night since sunlight may be visible because of refraction. Also, the time when the Sun is above the horizon at the poles is 186 days, the numerical asymmetry occurs because the time when the Sun is partially above the horizon is counted towards the daytime. Also, the numbers are average numbers, the ellipticity of the Earths orbit makes the South Pole receive a week more of Sun-below-horizon than the North Pole. As there are kinds of twilight, there also exist various kinds of polar night. Each kind of night is defined as when its darker than the corresponding kind of twilight. The descriptions below are based on relatively clear skies, so the sky will be darker in the presence of dense clouds. Polar twilight occurs in areas that are located at the border of the polar circles. There is then no true daylight at the culmination, only civil twilight. This means that the Sun is below the horizon, but by less than 6°, during civil twilight, there may still be enough light for normal outdoor activities because of light scattering by the upper atmosphere and refraction. Thus, polar twilight is limited to more than 66.5 degrees from the equator, in other words
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Zodiacal light
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Zodiacal light is a faint, roughly triangular, diffuse white glow seen in the night sky that appears to extend up from the vicinity of the Sun along the ecliptic or zodiac. It is caused by sunlight scattered by space dust in the zodiacal cloud, the zodiacal light decreases in intensity with distance from the Sun, but on very dark nights it has been observed in a band completely around the ecliptic. In fact, the light covers the entire sky and is responsible in large part for the total skylight on a moonless night. Another phenomenon—a faint, but slightly increased, oval glow directly opposite the Sun—is called the gegenschein, the dust forms a thick pancake-shaped cloud in the Solar System collectively known as the zodiacal cloud, which occupies the same plane as the ecliptic. The dust particles are between 10 and 300 micrometres in diameter, most with a mass around 150 micrograms, the zodiacal light appears as a column, brighter at the horizon, tilted at the angle of the ecliptic. This is why it is most clearly visible near sunrise or sunset, when the sun is blocked, the dust band that causes the zodiacal light is uniform across the whole ecliptic. The dust further from the ecliptic is almost undetectable except when viewed at an angle with the sun. Thus it is possible to see more of the width at small angles toward the sun, the source of the dust has been long debated. Until recently, it was thought that the dust originated from the tails of active comets, many of our meteor showers have no known active comet parent bodies. Over 85 percent of the dust is attributed to occasional fragmentations of Jupiter-family comets that are nearly dormant, Jupiter-family comets have orbital periods of less than 20 years and are considered dormant when not actively outgassing, but may do so in the future. The dust in meteoroid streams is much larger,300 to 10,000 micrometres in diameter, the Poynting–Robertson effect forces the dust into more circular orbits, while spiralling slowly into the Sun. Hence a continuous source of new particles is needed to maintain the zodiacal cloud, cometary dust and dust generated by collisions among the asteroids are believed to be mostly responsible for the maintenance of the dust cloud producing the zodiacal light and the gegenschein. Particles can be reduced in size by collisions or by space weathering, when ground down to sizes less than 10 micrometres, the grains are removed from the inner Solar System by solar radiation pressure. The dust is replenished by the infall from comets. Zodiacal dust around nearby stars is called exozodiacal dust, it is an important source of noise for directly imaging extrasolar planets. It has been pointed out that this exozodiacal dust, or hot debris disks, can be an indicator of planets, Zodiacal light is produced by sunlight reflecting off dust particles in the Solar System known as cosmic dust. Consequently, its spectrum is the same as the solar spectrum, the material producing the zodiacal light is located in a lens-shaped volume of space centered on the sun and extending well out beyond the orbit of Earth. This material is known as the interplanetary dust cloud, since most of the material is located near the plane of the Solar System, the zodiacal light is seen along the ecliptic
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Integrated Authority File
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The Integrated Authority File or GND is an international authority file for the organisation of personal names, subject headings and corporate bodies from catalogues. It is used mainly for documentation in libraries and increasingly also by archives, the GND is managed by the German National Library in cooperation with various regional library networks in German-speaking Europe and other partners. The GND falls under the Creative Commons Zero license, the GND specification provides a hierarchy of high-level entities and sub-classes, useful in library classification, and an approach to unambiguous identification of single elements. It also comprises an ontology intended for knowledge representation in the semantic web, available in the RDF format
